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  1. #1
    Senior Member sunburst's Avatar
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    physics, fenders and mud

    This really has very little to do with mt. biking, but who else is really going to really appreciate mud, besides you guys?

    This is about my recent decision to being car-free, and my new fenders, just installed Thurs, so I can cycle through the winter. Well, we had our first real rain Sat, but today (Sunday) was great so I cycled out to the farmer's market and took the long way home around the bay. Went off-road for fun and very quickly remembered that the levies around here turn into this thick sticky mud. I had street tires on my old rigid-fork Rockhopper so I thought I was cool with the mud. Plus my fenders were going to protect me - right?

    Within 30-40 feet I had collected so much mud I was slipping and sliding. A few feet more and I seized up. I mean the damned wheels wouldn't even turn - mud in the brakes, fenders, everywhere. And not a stick in sight! So I tried dragging the bike up a hill to a paved bike/pedestrian trail and the bike felt like it weighted at least half a ton more than normal. Finally got enough mud off it to start turning the wheels and eventually found a branch a quarter mile or so up the trail.

    So anyway, while brushing up on physics a few hours later (hey, what do you do in your spare time!?! - actually I'm just trying to help my son survive high school), I read this section on rolling vs sliding friction and the advantages of the wheel. From my old college text: "in rolling, the microscopic contact welds are 'peeled' apart rather than 'sheared' apart as in sliding. This will reduce the frictional force by a large factor."

    Oh.

  2. #2
    Blue Light Special kmart's Avatar
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    Pardon me, but what does that quote about peeling vs sliding friction have to do with the mud caked around your fenders and tires? I mean, I guess with all that mud stuck to you you're trying to "shear" mud instead of rolling over it, but at that point you probably aren't going very fast anyway because you've completely lost control.

    When you say street tires you mean slick treads right? Seems like a bad decision for mud - you'll cut right to the bottom of it start sliding around all over the place. Put some knobby tires on, the fatter the better, and try that muddy section again.
    Last edited by kmart; 11-03-08 at 01:23 AM.
    Quote Originally Posted by KrisPistofferson View Post
    racer x flies across cobblestones with a grimace of determination, three feet of seatpost, bars level with ankles, carbon fiber frame with Kryptonite lugs and a millimeter clearance between the fork and the 700x21c tires. This gives everyone a *****

  3. #3
    Senior Member sunburst's Avatar
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    You're right, sliding/peeling got nothing to do with the fenders, except that the mud in the fenders stopped the wheels. The sliding happened when the wheels stopped turning and I tried to drag the bike along the trail. I know I had the wrong tires. I wasn't thinking about mud when I started off-road because most of the trail is pretty decent gravel hardpack.

  4. #4
    Senior Member sunburst's Avatar
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    xx
    Last edited by sunburst; 11-03-08 at 08:24 PM.

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